Cathode heater



Dec. 29, 1959 0. F. RILEY EI'AL CATHODE HEATER s Sheets-Sheet 1 Filed Jan. 22, 1957,

FIG.

IN V EN TORS DANIEL F. R'LEY SEYMOUR GOLDBERG BY z ,a/v-v AT T ORNE Y5 Dec. '29, 1959 Filed Jan. 22, 1957 D F. RILEY ETAL 2,919,373

CATHODE HEATER 3 Sheets-Sheet 2 FIG. 4

FIG. 5

INVENTORS,

DANIEL F. RILEY SEYMOUR GOLDBERG BY W ATTORNEYS Dec. 29, 1959 Filed Jan. 22, 1957 FIG. 6

' D. F. RILEY ETAL CATHODE HEATER 3 Sheets-Sheet 3 INVENTORS. DANIEL F. RILEY SEYMOUR GOLDBERG AT ORNEYS CATHO'DE-HEA'IER Daniel F. Riley, South-Braintree, and Seymour Goldberg, Lexington, Mass., assignors to Edgerton, Germeshausen & Grier, Inc., Boston, Mass, a corporation of Massachusetts ApplicationJanuaryZZ, 1957, Serial N0.-635,203 9 Claims. ((31. 3134-340 The present invention relates to electric-discharge devices and, more particularly, to improved cathode heaters for use in gaseous-discharge tubes and the like.

In many gaseous-discharge devices, such as, for example, hydrogen thyratrons, the cathodes are of the socalled indirectly heated type, containing independent heating means for bringing the cathode up'to operating temperatures. The heater is normally a coil of tungsten wireplaced within or immediately adjacent to the cathode. Heat from this heater is radiated or-conducted to the cathode proper. It is generally required that the heater be coated with an insulating coating to avoid making electrical contact between adjacent turns or, in cases where the heater is in physical contact with the cathode, to avoid making electrical contact therewith. The process by which the insulating coating is applied to the heater involves spraying, painting orotherwise depositing upon the heater a suspension of refractory oxide particles in a suitable binder. This coating is then usually fired to a -hightemperature (about 1700 C. for aluminum oxide) to sinter the deposit to the heater base metal and to render the coating tough and adherent. In the process of such high-temperature firing, however, tungsten undergoes certain metallurgical changes in regard to its crystal structure making it extremely brittle and fragile. Cathode heaters so constructed sometimes can not withstand high shock and vibration conditions. Furthermore, because of their small heat radiating and conducting surface, such cathode heaters must be operated at relatively high temperature in order to maintain their associated cathodes at the required operating temperatures. The following of alternating current in such a cathode heater, moreover, creates magnetic fields which introduce hum and jitter during operation of the tube. Such disadvantages are particularly serious when cathode heaters are employed in gaseous-discharge devices of the type disclosed in copending application Serial No. 580,551 filed April 25, l956by Kenneth J. Germeshausen and Seymour Goldberg for Electric-Discharge Device and Cathode, wherein-a multi-vane type of cathode is employed and elficient use of the total volume of the heater chamber is difficult.

It is an object of the present invention, accordingly,

to provide a new and improved cathode heater.

An additional object is to provide such a heater that will withstand extremely high shock and vibration conditions.

A further object is to provide a cathode heater with greater heat-radiating and conducting surface area.

A further object, still, is to provide a cathode heater in which the back-and-forth current-path magnetic fields resulting from alternating heater current tend to be cancelled, thus alleviating the jitter and hum heretofore associated withheater magnetic fields so generated.

Other and further objects will be explained'hereinafter and will be more particularly pointed'out in the appended claims. In summary, however, the present invention resides in the provision of a cathode heater comprising a .stantially parallel to one another.

stantially circular ,oroval .peripheral contour.

"ice

--2 thin preferably sheet-metal planarstrip successively disposed predetermined portionssof which are substantially parallel to, though spacedfrom, one .another and lie in a common plane, The strip is preferably coated withan insulation coating throughout. Preferred constructional details arehereinafter. explained.

The invention will nowhedescribed inconnection with the accompanyingdrawings,

Fig. 1 ofwhich isaplan view of a cathode heater embodying the invention in preferred form and partly broken away to illustrate details of construction;

Fig. 2 is an enlarged sectional perspective .of Fig, 1 taken along theline 2 ..2 thereof, looking in the direction of the arrows;

Figs. 3, 4 and 5 areplan .views of modified cathode heater constructions; and

Fig. 6 is an explodedperspective view of a cathode and heater of the type illustratedin Fig. .1, showing details .of construction and assembly.

Referring .to Figs. 1 and 2,.the cathode heater comprises apreferably zig-zag .strip 1 of suitable substantially planar material of desired thickness, such as sheet molybdenum. The successive portions or legs "15, 16, 17, 18, 19 2.0.,of thestrip are substantially co-planar and extend in opposite directions, being preferably sub- The successive portions may be of different lengths so as to provide a .sub-

The space between the sueeessivepbrtions, however, is preferably substantially uniform, asshown at 4. The strip may,

for example, be formed by cutting, stamping or votherwiseforming.the.,interstices 4 froma flat sheet. An insulatingcoating 3-of .suitable (material, such as'for example, alumina, is appliedthroughout the .exposed surface area of all-dimensions of the. strip, as more particularlyshown in Fig. 1. The fireeends or .terminals8 and phuric acidand 40-percent distilled water, :to dissolve the same in a gradual vmanner,periodically washing the-same with distilled water and checkingthe resistance until the proper resistance valve isobtained. The insulating coating 3 :maythenbeappliedby Ihe sintering and'firingproo ess heretoforefdescribed. For. morerugged construction, however, the molybdenu m or otherstrip ispreferably maintained at room temperature and atomized molteninsulating material, :such .as alumina issprayed thereon in such manner'that said particles of insulating material are still in molten-particleformuponimpacting said molyb denum surface. By this latter process, the high temperature firing is avoided and the heater strip thereby retains its ductile,enonabrittle,.uncrystallized nature, thus greatly aiding .assemblyzand spotewelding of the heater to the cathodetstructure. aswell ,as improving general ruggedness.

A particular ,advantagepf this type of construction resides in the-factthat iit provides a -maximum heat radiatingand conducting surface area,-thus reducingthe heater p t ng t mperature ne e s y o b n a .quired cathode gternperature and ethereby -resulting in longer heater life. and more reliable operation. A further advantage: resides inv ,the -,fl at, planar circular-contour conf guration of, :gthe..--hea t er' :1, 3.

v This configuration permits the use of a cylindrical heater chamber design of minimum volume. As more particularly illustrated in Fig. 6, the substantially planar heater 1, 3 may be inserted in a shallow cup 7. with the terminal welded or otherwise electrically secured to a point 6 on the inside surface of cup 7 and with the other terminal 8 extending through an aperture 11 of cup 7. The terminal 8 may be connected to one terminal of source of alternating-current heater potential and the cup 7 may be connected to the other or preferably ground terminal. The cathode assembly, comprising a cathode disc 12 to opposite surfaces of which cathode electron-emitting vanes 14, shown as spaced concentric cylinders as described in the said copending application, and a spacer ring 13 have been brazed, is then fitted into, the cup 7 in such a manner that the spacer ring 13 and cathode disc 12 do not make physical contact with the cathode heater 1, 3. The cathode disc 12 and the spacer ring 13 may then be spot-welded to the cup 7 thus providing a rugged assembly suitable for applications wherein high shock and vibration conditions are present. Still a further advantage that inures to this type of construction is the fact that the planar configuration'of the heater 1, 3 results in a weaker overall magnetic field. In addition, the back-and-forth current-path magnetic fields generated by the alternating heater current passing in opposite directions along successive portions 15, 16 20 of the heater 1, 3 tend to cancel one another, thus alleviating such difficulties as hum and jitter normally associated with alternating-current-operated heater filaments of heretofore known configurations.

The cathode heater of the present invention is, of course, useful in other than the particular dischargedevices before referred to. It may, as but two further illustrations, be employed in gaseous diodes or thyratrons of other construction. Other cathode heater configurations than the particular configuration of Figs. 1, 2 and 6 may also be employed. It is not, for example, essential that the cathode heater be of circular peripheral configuration, as discussed in connection with the embodiments of Figs. 1, 2 and 6, though, as before mentioned, such a configuration gives rise to advantages in heater-chamber design. It may, for example, be of other peripheral configuration, such. as of rectangular form, Fig. 3, having substantially equal-length legs or portions. As another example, the heater may be constructed in spiral form 3', Fig. 4, having a single long spiral interstice 4. The terminals 8' and 10 will then be disposed respectively at the center and the periphery of the heater. As still a further illustration, two spiral heaters 3, of the type illustrated in Fig. 4, may be welded together at their centers 5, as illustrated in Fig. 5, to provide interwoven, spiral conducting strips extending parallel in opposite directions. The same result may be obtained by stamping out a double spiral 3'- from a single flat sheet of conducting material 1. Such a configuration, moreover, results in still further reduction of the magnetic field generated in heaters of spiral configuration.

Further modifications will occur to those skilled in the art and all such are considered to fall Within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane, the strip being covered throughout with an insulating coating only.

2. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane, the successively disposed portlons being of different dimensions so as to provide a substantially oval peripheral contour, and the strip being covered throughout with an insulating coating only.

3. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar spiral strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane, the strip being covered throughout with an insulating coating only.

4. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar strip of sheet metal successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane.

5. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar strip of sheet molybdenum, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane. a

6. A cathode heater of predetermined electrical resistance comprising a continuous substantially planar strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane, the strip being covered throughout with an alumina coating.

7. A cathode construction having, in combination, a cathode comprising a base member carrying electronemitting surfaces extending from the base member on one side thereof, and a cathode heater disposed on the other side but out of contact with the base member and of predetermined electrical resistance comprising a continuous substantially planar strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane.

8. A cathode construction having, in combination, a cathode comprising a base member carrying electronemitting surfaces extending from the base member on one side thereof, and a cathode heater disposed on the other side but out of contact with the base member and of predetermined electrical resistance comprising a continuous substantially planar strip of conductive material, successively disposed predetermined portions of which are substantially parallel to, though spaced from, one another and lie substantially in a common plane, the strip being covered throughout with an insulating coating.

9. A cathode construction having, in combination, a cathode comprising a base member carrying electronemitting surfaces extending from the base member on one References Cited in the file of this patent UNITED STATES PATENTS 2,010,463 Pratt Aug. 6, 1935 2,057,931 Stupakotf Oct. 20, 1936 2,391,927 Segerstrom Jan. 1, 1946 2,504,335 Ionker Apr. 18, 1950 

